The present invention relates to a metal mold cooling device, and more particularly, to such device capable of introducing sufficient amount of a cooling liquid into a cooling hole of the metal mold, the hole having relatively small diameter.
Cooling to the metal mold at every predetermined cycle is required so as to produce desirable cast products. To this effect, conventionally, a cooling liquid such as a water is ejected into a cooling hole formed in the metal mold so as to remove evaporation heat therefrom. For example, according to the metal mold cooling technique disclosed in Japanese Patent Application Kokai Nos. 61-108462 and 63-299848, a pipe connected to an air source is inserted into the cooling hole drilled into the metal mold, and a water supplying pipe branched from the pipe is connected to a water tank. Water in the water tank is introduced into the pipe through the water supplying pipe by making use of a negative pressure generated within the pipe for ejecting the water at a tip end of the pipe.
Japanese Patent Application Kokai No. 60-72641 discloses improvement in a metal mold temperature control in which a cooling passage is provided in the metal mold for selectively ejecting one of liquid, gas(air) and liquid/gas mixture into the passage. To this effect, a cooling pipe is connected to an inlet opening of the cooling passage, and the cooling pipe is branched into first branch pipe to which a liquid tank is connected and a second branch pipe to which an air tank is connected. The first and second branch pipes have first and second change-over valves, respectively. By controlling valve opening timing of these change-over valves by means of a timer, one of the liquid, gas and liquid/gas mixture is selectively introduced into the cooling passage.
However, in the device disclosed in the Japanese patent application Kokai Nos. 61-108462 and 63-299848, cooling liquid ejection from the ejection opening of the pipe is only achievable in a case where a cross-sectional area of the pipe is greater than that of the water supplying pipe. It is impossible to perform water ejection if the cross-sectional area of the pipe is smaller than that of the water supplying pipe. Therefore, if the pipe has a small cross-sectional area, the cross-sectional area of the water supplying pipe must be designed to be further smaller than that of the pipe. As a result, insufficient cooling water supply results. Particularly, if the cooling hole has an extremely small diameter to such extent of a tip end portion of a cast removal pin, such drawbacks is brought into highlighted problem.
In the device disclosed in the Japanese Patent Application Kokai No. 60-72641, if only the cooling liquid such as water is supplied into the metal mold cooling passage in a case where the latter has the small diameter, the water is evaporated within the passage, thereby increasing the pressure in the passage. Thus, subsequent cooling liquid cannot be introduced into the passage. Further, in supply of the liquid/gas mixture, if the pneumatic pressure is greater than the hydraulic pressure, cooling liquid supply may be restrained, and reversely, if the hydraulic pressure is greater than the pneumatic pressure, air supply may be restrained. Accordingly, fine temperature control to the metal mold may not be achievable. In order to obviate this drawback, pressure control units are respectively required in the liquid tank and the air tank, which in turn, renders the overall device intricate.